The present invention relates to a magnetic circuit with a coil, and a method of making such a circuit.
Magnetic circuits with coils are used in many fields including those relating to current sensors and transformers. In applications such as current sensors, measurement precision is closely related to the magnetic properties of the materials used and to the manufacturing precision. Attaining a specified precision is often in conflict with the need to reduce manufacturing costs and the size of components.
A method of manufacturing a coil on a tore-shaped magnetic circuit is described in European patent EP 668 596. The method described in this patent, which attempts to respond to the above mentioned criteria, comprises the steps of winding a conducting wire coated with a thermo-adhesive around a cylindrical mandrel to form a coil, opening a magnetic circuit by separating ends thereof forming the air-gap, sliding the coil onto the magnetic circuit and subsequently closing the magnetic circuit.
This conventional method has a number of disadvantages. Firstly, it is very difficult to remove the coil from the cylindrical mandrel and thereafter insert it on the core. Secondly, opening and closing the magnetic circuit, as in any plastic deformation, deteriorates the magnetic properties of the circuit.
In view of the above disadvantages, the object of the present invention is to provide a magnetic circuit with coil having a precise electrical and magnetic behaviour and which may be manufactured industrially in a economic manner.
Objects of the invention have been achieved by a method of making a magnetic circuit with coil according to claim 1, a magnetic circuit with coil according to claim 5, and a device for manufacturing a magnetic circuit with coil according to claim 8.
In the present invention, a method of making a magnetic circuit with coil having an electrical coil and a magnetic core comprises the steps of making a coil by winding a conducting wire on a mandrel having a slightly conical exterior surface, and inserting the coil on a magnetic core in the form of an open spire, said spire being formed before providing the magnetic material thereof with its specific magnetic properties. After insertion of the coil on the magnetic core, ends of the core are deformed in a direction substantially orthogonal to the plane of the magnetic circuit to bring them closer together. Advantageously, through this method, the magnetic material is deformed minimally in order to avoid degrading its magnetic properties.
The coil may be inserted on the magnetic core during its removal from the mandrel, which reduces the time and cost of manufacturing the magnetic circuit with coil. In this respect, it is advantageous to insert an end of the magnetic core in a cavity at an end of the mandrel to facilitate insertion of the coil on the magnetic core.
The magnetic circuit with coil may further comprise an end plate and a connector, the end plate and the connector each arranged at a respective end of the coil, the coil being mounted on the magnetic core formed of a tore-shaped magnetic wire. The end plate facilitates insertion of the coil on the core by virtue of its shape and dimensions and by reducing the coefficient of friction. To this end, the end plate may advantageously have a chamfered inner surface to facilitate following the curvature of the core. The end plate also protects the electrical wire from damage to its insulation layer by rubbing against the tore.
The mandrel of the device for making the magnetic circuit with coil, around which the coil is formed, may comprise a slightly conical exterior surface. This facilitates removal of the coil from the mandrel.
The angle xcex1 of the cone may be very small, for example having a value tan xcex1 situated between 0.001 and 0.01. The difference in diameter of the coil between ends thereof is therefore negligible.
The mandrel may further comprise a cavity at its free end to enable insertion of an end of the magnetic core therein, thereby facilitating assembly of these components.
Other objects and advantageous features of the invention will be apparent from the description and claims hereafter, and from the annexed drawings.